1. Field of the Invention
The present invention relates to a robot controller that controls a tandem arc welding system that performs arc welding by causing a welding torch to move so as to track a weld line while the welding torch is caused to weave leftwards and rightwards using a robot along a V-shaped or an L-shaped groove or a groove that is similar to the V-shaped or the L-shaped groove. The welding torch includes two electrodes. In addition, the present invention relates to an arc tracking controlling method using the robot controller, and a tandem arc welding system.
2. Description of the Related Art
As a related technology regarding arc tracking when carrying out related tandem arc welding, for example, a technology discussed in Japanese Unexamined Patent Application Publication No. 2008-93670 is provided. In this technology, arc tracking is performed by calculating a correction amount from amounts of electrical changes of a leading electrode and a trailed electrode in one weaving period. In addition, in this technology, the arc tracking is carried out by rotating the trailed electrode around the leading electrode. That is, in the related arc tracking performed during the tandem arc welding, the arc tracking of the trailed electrode is carried out to perform correction around a leading electrode torch. Accordingly, it is necessary to set the rotational center, that is, a tool center point (TCP) at the leading electrode.
Here, the tandem arc welding that is performed using a robot that performs the welding is carried out by previously teaching a work trajectory and reproducing the stored trajectory. The teaching of the work trajectory is performed after specifying the aforementioned TCP. In a tandem arc welding system, the position of a wire end of the leading electrode, the position of a wire end of the trailed electrode, and a position between the electrodes are previously set as angles and distances from a flange surface of the robot, and are changeable according to the conditions.
In the tandem arc welding, setting the TCP at an intermediate position between the leading electrode and the trailed electrode may be advantageous from the viewpoint of operation. For example, as shown in FIGS. 9A and 9B, changing a direction of operation of the robot applies to such a case. As shown in FIG. 9A, when the TCP is set at the leading electrode 2a and this is taught, if the direction of operation is changed to the opposite direction without changing a teaching position, an end point changes by a distance S. Therefore, the welding torch and a welded structure interfere with each other, thereby making it necessary to correct the teaching position. In contrast, as shown in FIG. 9B, when the TCP is set at an intermediate position between the leading electrode 2a and the trailed electrode 2b, and this is taught, even if the direction of operation is changed to the opposite direction without changing a teaching position, an end point does not change. Therefore, the amount of correction of the teaching position is reduced.
However, when, for example, in the arc tracking discussed in the aforementioned Japanese Unexamined Patent Application Publication No. 2008-93670, the TCP is set at a position other than where the leading electrode 2a is disposed, such as an intermediate position between the leading electrode 2a and the trailed electrode 2b, the following occurs. That is, as shown in FIG. 10A, the arc tracking of the trailed electrode 2b rotates around the intermediate position between the leading electrode 2a and the trailed electrode 2b (corresponding to the TCP) as a rotational center, so that the position of the leading electrode 2a changes as a result of the arc tracking of the trailed electrode 2b. When the position of the leading electrode 2a changes during arc welding in this way, locations that actually need to be welded are not welded. This may result in defective welding, such as weld penetration. Therefore, in the arc tracking discussed in the aforementioned Japanese Unexamined Patent Application Publication No. 2008-93670, in order to minimize defective welding, it is necessary to set the TCP at the leading electrode 2a and correct the teaching position as shown in FIG. 10B.